Minerals

Chapter 3

What is a Mineral?

Mineral Characteristics

Naturally occurring Inorganic Solid Definite chemical composition

Either elements or compounds Have orderly arrangements of

atoms Crystalline/Set atomic pattern

The Structure of Minerals Crystals Solids in which the atoms are

arranged in orderly, repeating patterns. Minerals are classified into six

major crystal systems according to their crystal structures: Hexagonal Cubic Tetragonal Orthorhombic Monoclinic Triclinic

The Structure of Minerals Formation of

Crystals:

From the cooling and solidification of magma The type and amounts of elements

present in the magma partly determine which minerals will form.

How rapidly the magma cools determines the size of the crystals. Slow – large Fast – little

From the evaporation of a solution or the supersaturating of a solution

Mineral Compositions and Groups Mineral

Classification

2 Main Groups: Silicates

Minerals that contain silicon and oxygen

Contain most of the common rock-forming minerals

Nonsilicates Do not contain silicon

Mineral Compositions and Groups Mineral

Amounts:

About 4,000 different mineral are found on Earth. Only a few dozen of these minerals

are common. 90 elements occur naturally in

the crust of the Earth. ~98% of the crust is made of only

eight elements. Silicon and Oxygen are two of

the most abundant elements found in Earth’s crust.

Identification of Minerals Hardness A measure of how easily a

mineral can be scratched Measured on a scale of 1 to 10

called the Mohs Scale. 10 = hardest, diamond 1 = softest, talc Iron nail = 4.5 Fingernail = 2.5

Identification of Minerals Luster The way a mineral reflects light.

Metallic or nonmetallic

Identification of Minerals Specific

Gravity

Ratio of the weight of the mineral with the weight of an equal volume of water.

Specific gravity of minerals can be roughly relatively tested using heft.

Identification of Minerals Streak Color of a mineral in a powder

form Found by rubbing the mineral

across a porcelain streak plate

Identification of Minerals Cleavage Mineral breaks along smooth,

flat surfaces Due to the atomic arrangement of

the mineral

Identification of Minerals Fracture Fracture

Mineral breaks along rough, uneven, or jagged surfaces.

Identification of Minerals Color and

Appearance

Color and Appearance Highly unreliable.

Identification of Minerals Other

Properties

Other properties Magnetic Optics Chemical reactions

Gems Properties of

Gems

Gemstones are highly prized minerals because they are rare and beautiful. Most gems are special varieties of

a particular mineral. Clearer, brighter, or more colorful Have a slightly different chemical

formula: Amethysts are quartz with a trace

amount of iron. Have a better crystal structure.

Gems Important

Gems

Cullinan Diamond Largest uncut diamond discovered Found in South Africa in 1905 3,106.75 carats (621 g) Cut into 9 main stones and 96 smaller stones Largest of these, the Great Star of Africa

(530.20 carats) is part of the British crown jewels.

Hope Diamond Purchased by Henry Philip Hope around 1830. 45.52 carats (9 g) All Hope’s family plus a later owner suffered

misfortune. Currently on display in the Smithsonian.

Gems Useful Gems Diamonds

Used as industrial abrasives and cutting tools

Rubies Produce certain types of laser light

Quartz Used in timepieces and electronics

Useful Elements in Minerals Ores A mineral or rock that contains a

useful substance that can be mined at a profit Examples:

Iron is found in the ores hematite and magnetite

Aluminum is found in the ore bauxite

Useful Elements in Minerals Extracting

Elements

Refining Wanted element is separated from

unwanted materials. Smelting

The substance is melted to separate it from any remaining unwanted materials.

Useful Elements in Minerals Vein Minerals Occur when dissolved metallic

elements travel in fluid form through weaknesses in rock and form mineral deposits.

Useful Elements in Minerals Titanium Found in ilmenite and rutile.

Lightweight and durable Used in auto body parts, aircraft,

eyeglasses, etc.